1. Field of the Invention
The present invention concerns a method for the metallization of a luminescent screen. More particularly, it concerns a method for depositing an organic film, removable by heat, on the luminophors of a luminous screen used especially in color television tubes or color display monitors.
2. Description of the Prior Art
Luminescent screens are generally made by depositing, on the inner face of a glass face plate, small crystals of a cathodoluminescent body. These are called luminophors. To improve luminance particularly, the screen is moreover coated with a thin film of a metallic material, preferably aluminium. To make it possible to deposit the metal in the form of a continuous thin film, the luminophor grains are, first of all, coated with a removable film. This film is then destroyed by burning in air. Different materials can be used to make the film. Thus, as described in the U.S. Pat. No. 3,582,390, the film can be got from a resin-based aqueous emulsion so as to produce an organic substrate which is volatilized during subsequent burning. However, this type of emulsion gives a non-continuous film having holes, and the aluminium layer deposited on this film has low reflectivity. The luminance of the tube thus obtained is therefore weaker than is the case when other materials, notably solvent-based lacquers, are used to make the film. To overcome this drawback, the U.S. Pat. No. 3,579,367 has proposed a double layer method which reduces the luminance losses of the tube. However, in this method, two different acrylic emulsions are used, each having a particular TUKON hardness and a specific volatility. The use of two different precisely chosen emulsions is aimed at preventing any destruction or cracking of the aluminium film during subsequent burning. However, this method is costly and lengthy, and calls for highly sophisticated manufacturing systems when entirely automated production is desired.